Regice, The Iceberg Pokémon. Research revealed that its body is made of the same kind of ice that is found at the South Pole. It's body was made during an ice age. The deep-frozen body can't be melted, even by fire. It controls frigid air of minus 328 degrees F. Things will freeze solid just by going near it.

Battle Moveset

A Good Moveset for Regice would have to be this:

Attacks:

Ice Beam
Thunderbolt
Thunder Wave
Explosion OR Rest

Items Attached:

Leftovers

Preferred Nature:

Calm

Strategy Using Regice

Being one of the few ice types in the game, it has
only one resistance; ice types. As you may notice,
Regice's special defense is very high and it will
survive the majority of special moves used against it
(you could add Amnesia on Regice to boost this even
further, though this could just trigger a switch to a
physical sweeper that will defeat the purpose of a
special wall)
Its special attack isn't too bad either, allowing it
to use Bolt-Beam, which as stated in the counter, is
only resisted by Magneton and Lanturn.
Thunderwave will certainly make up for the lack of
speed when it reduces your opponent's speed in half
and gives you a 25% chance for a free turn or it may
force your opponent to switch.
Even though Regice may have a low attack stat,
Explosion will still do a lot of damage. Rest is
another possibility, since the nature is usually minus
attack.

EV Corner:

Max out the EVs in Special Attack & HP for Regice with any remaining in Special Defense

Strategy Against Regice

Regice is potentially the best Special Sponge
available. When caught of guard with a Physical Attack
it can survive it and it has Average HP and well above
average Special Defence. It has the Bolt-Beam combo
(which is only resisted by Magneton and Lanturn) and
also access to Thunder Wave which can be incredibly
annoying.
- Firstly, don't expect to automatically knockout
Regice with physical attacks. Even without defensive
EV's it is more than capable of surviving them (unless
you are attacking with very high base attack and a
Fighting, Steel or Rock attack). A Pokémon such as
Machamp (who can outrun Regice even with such low
speed) using Cross Chop can put a pretty bad hurting
on Regice's HP.
- Alternatively, you could stall with Thunder Wave and
Confuse Ray and slowly pick away at Regice, although
this may take a while and you are at risk of losing
all your efforts to Rest.
- Obviously, there is also the Seismic Toss and Night
Shade options available, which will KO Regice in 3-4
hits, although this is pretty slow and leaves you
exposed to it's offences, so this is best done with
some form of stalling in use.

Contest Moveset

A good Contest Moveset for Regice would have to be this for the Beauty Contest best with Modest, Mild, Rash or Quiet Nature:

Attacks:

Hail
Ice Beam
Blizzard
Explosion

Items Attached:

Blue Scarf

Strategy Using Regice

If you do the attacks in this following order you should have very few problems; 1st - Hail, 2nd - Ice beam, 3rd - Hail, 4th - Ice beam, 5th - Explosion